28O INEZ WHIPPLE WILDER. 



region (Fig. 8, a), undoubtedly the process of cell proliferation 

 which results in the formation of the longitudinal folds. 



With equally rapid strides does the histogenesis of the intestinal 

 region occur during the brief terrestrial period of larval life, 

 until from the large yolk mass which fills and distends the body 

 cavity of the newly hatched larva and furnishes nutriment for 

 the rapidly growing animal, there is developed the entire length 

 of intestine with its convoluted windings, ready for the digestion 

 and absorption of ingested food material. 



The changes in the external form of the intestinal region in- 

 volved in this process may be demonstrated by comparison of the 

 dissections shown in Fig. 9, from which it will be seen that 

 there is gradually moulded out of the intestinal yolk mass a 

 loop forming an 6"-shaped figure which consists of an anterior 

 portion lying upon the right side, into which the duodenum 

 opens, and a posterior portion lying upon the left side, from which 

 the rectum leads. Both of these regions, particularly the left 

 and more posterior loop, are for a considerable time enlarged 

 through the presence of the remaining yolk material as indicated 

 by the condition shown in stage F, (Fig. 9, d) the oldest of the 

 terrestrial larvae. Gradually, however, concomitant with the 

 consumption of the last remnants of yolk material and the 

 consequent diminution in the diameter of the intestine, there 

 occurs a still further increase in its length, so that each of the 

 two main loops acquires two or three subsidiary ones variable, 

 of course, in relative position with constantly varying peristaltic 

 conditions (cf. Fig. 9, e,f, g, and h). 



The last part of this process of differentiation of the intestine 

 is apparently not usually accomplished until after the larva has 

 reached the water, since frequently in the early fall aquatic larvae 

 are found with the intestine in the condition shown in d, e and /, 

 Fig. 9, exactly similar to the condition found in my oldest ter- 

 restrial stage F. Food may be ingested many days previous to 

 the final disappearance of the yolk; in fact, the stomach of one 

 specimen of stage C (terrestrial larva, average age 3 days and 

 greatest possible age 5 days) contained a small copepod, while 

 there was another in the intestine; and the specimen of stage D, 

 from which the dissection shown in Fig. 9, C, was made, had 30 



